1. Field of the Invention
The invention relates generally to hydrofoil sailboats and more particularly to a novel sailing frame that greatly increases the speed and improves the balance and stability of such craft, and especially the ability to tack quickly and readily, in connection with which a novel hull and method of tacking are disclosed.
2. Description of the Related Art
The quest for a hydrofoil sailboat capable of attaining high speeds even in low winds with a shallow draft and carrying reasonably high payloads has been long lived. One of the milestones in this arduous quest was a book entitled "The 40-Knot Sailboat" written in 1963 by one of the present applicants and published by Grosset and Dunlop, New York, NY. To date, although several attempts have been made by the present applicants and numerous other skilled inventors to achieve all of these desirable operational capabilities, no single sailboat has been designed or built that has satisfied the necessary criteria.
Conventional monohull state-of-the-art sailboats suffer from the following limitations: they do not sail well at less than 30.degree. to the true wind; they have a significant leeward vector above the center of gravity of the craft requiring a ballasted keel or moveable ballast which increases displacement and wetted surface area, thus increasing drag, and the ballast may produce a net negative buoyancy which reduces their safety; they are slow and difficult to tack under certain conditions; the maximum speed of a displacement vessel is constrained by wave drag and so cannot exceed hull speed, approximately 1.34 times the square root of the waterline length; and they sail at a greatly heeled angle in strong winds, creating among other difficulties insecure footing for people sailing them.
In the case of conventional windsurfers, the sail does not afford stabilization of the hull, making them difficult to sail in strong gusts. They are difficult to sail because of the balancing skills that must be learned and because they have no rudder. They are extremely limited in the sail area they can carry because live ballast is required.
The evolutionary steps made toward solving the above-noted operational problems and overcoming undesirable characteristics are shown in U.S. Pat. No. 3,094,961, issued Jan. 25, 1963; U.S. Pat. No. 3,295,487, issued Jan. 3, 1967; U.S. Pat. No. 3,631,828, issued Jan. 4, 1972; U.S. Pat. No. 3,646,902, issued Mar. 7, 1972; U.S. Pat. No. 3,981,258, issued Sept. 21, 1976; and in U.S. Pat. No. 4,228,750, issued Oct. 21, 1980. All of these patents were granted to Bernard Smith, one of the present applicants, and are hereby incorporated by reference herein.
The cited patents provide a discussion of the structure, dynamic forces, and controls of one particular variety of hydrofoil sailing frame. Although each of the aerohydrofoils and hydrofoil sailboats disclosed possessed certain desirable features, all suffered from one or more deficiencies that limited their commercial acceptance.
For example, the hydrofoil sailboat disclosed in U.S. Pat. No. 3,981,258 employs a slender hull with one flat side facing the foil-shaped sail and one convex side facing away from the sail. The sail is supported at its base ends by a pair of freely swiveling waterskis, and a ruddering hydrofoil is disposed at each end of the specially shaped hull. A crank is adjusted to take up or release the cables that position the ruddering hydrofoils, and the sail is inclined from the vertical to eliminate listing moments.
The hydrofoil sailboats patented by Smith prior to the sailboat shown in U.S. Pat. No. 3,981,258 suffered from one or more of the following defects: severely limited load-carrying capacity, unsatisfactory performance in low wind, and inordinate draft, making such craft unsuitable for shallow water or beaching operations. Although the waterski sailboat disclosed in U.S. Pat. No. 3,981,258 solved most of the problems encountered with the hydrofoil sailboats disclosed in the earlier Smith patents, its control system proved too cumbersome in strong winds, requiring excessive manual force and dexterity. Moreover, the hydrofoils attached to the bow and stern of the hull of the waterski sailboat could not be conveniently inclined to supply additional lift at high speed.
In U.S. Pat. No. 4,228,750 the craft described was difficult to sail, tack, and control in varying conditions. Also, the windward foil had a downward vector when it was backwinded, preventing tacking.